The disclosure herein relates to structures and methods for making structures having metallic rails about a composite structure. More specifically, the disclosure describes methods for making composite fan cases having a metallic rail disposed thereabout.
In gas turbine engines, such as aircraft engines, air is drawn into the front of the engine, compressed by a shaft-mounted compressor, and mixed with fuel in a combustor. The mixture is then burned and the hot exhaust gases are passed through a turbine mounted on the same shaft. The flow of combustion gas expands through the turbine which in turn spins the shaft and provides power to the compressor. The hot exhaust gases are further expanded through nozzles at the back of the engine, generating powerful thrust, which drives the aircraft forward.
Because engines operate in a variety of conditions, foreign objects may undesirably enter the engine. More specifically, foreign objects, such as large birds, hailstones, sand and rain may be entrained in the inlet of the engine. As a result, these foreign objects may impact a fan blade and cause a portion of the impacted blade to be torn loose from the rotor, which is commonly known as fan blade out. The loose fan blade may then impact the interior of the fan casing causing a portion of the casing to bulge or deflect. This deformation of the casing may result in increased stresses along the entire circumference of the engine casing.
In recent years composite materials have become increasingly popular for use in a variety of aerospace applications because of their durability and relative lightweight. Although composite materials can provide superior strength and weight properties, and can lessen the extent of damage to the fan casing during impacts such as blade outs, designing cases that are capable of both withstanding internal impacts, as well as supporting hardware mounted on the external surface.
Laminated composite structures generally have superior strength in-plane due to the presence of continuous reinforcing fibers. However, issues may arise when attaching a secondary structure about the body of the composite structure, as opposed to about an end of the composite structure. Secondary structures and instrumentation are often utilized during the design and testing of an engine, and must be attached to the composite fan case. Drilling of additional holes in a composite fan case is undesirable as this weakens the structure at the point of the aperture. Alternately, using a metallic fan case to support the additional external testing hardware allows for adequate support, but the case does not maintain the same lightweight properties as a composite structure. Thus, there exists a need for composite fan case structure capable of withstanding both internal and external forces.